Mechanical Performances Analysis And Parameters Design Optimization Of The Aerostatic Bearing With Orifice Type Restrictor

The aerostatic bearing is a kind of gas-lubricated component which is developed based on the gas lubrication technology.Due to high motion accuracy,low friction and low heat generation,the aerostatic bearings are widely adopted in ultra-precision machining or measuring facilities.Among several kinds of restrictors used in the aerostatic bearings,the orifice type restrictor has got the widest application.Currently,the aerostatic bearings with the orifice type restrictor are still in continuous development.The mechanical performances of the bearing directly influence the machining capability or measuring precision of corresponding ultra-precision facilities.Hence,in the bearing design,the suitable bearing parameters should be designed to achieve the finest bearing performances.By this way,the performances of the ultra-precision facilities can also be enhanced consequently.The concentrated bearing mechanical performances mainly include the load carrying capacity,static and dynamic stiffness,damping,and the internal flow excitation related characteristics such as the micro-vibration.However,the mechanical performances analysis and parameters design optimization methods for the aerostatic bearing with orifice type restrictor are still need to be improved currently.Firstly,the occurrence mechanism of micro-vibration of the aerostatic bearing system should be further investigated,and the method for suppressing the micro-vibration should be developed.Secondly,the aerostatic journal bearing possesses complicated structural configuration and related air film geometry,the effective analysis method for the journal bearing mechanical performances is needed.Thirdly,the design optimization of the aerostatic bearing is still for the static performances currently,while the dynamic performances are not considered in optimization to improve the capability of resisting the dynamic load.For both static and dynamic performances,the optimization modeling method should be further investigated.To improve the mechanical performances of the aerostatic bearing with the orifice type restrictors,the influence rules of the bearing parameters on both static and dynamic performances are analyzed numerically.Based on the analysis results,the multi-objective optimization method is proposed and the design parameters are optimized.The main content includes:The restriction characteristics of the orifice-type restrictor and the occurrence mechanism of the bearing micro-vibration.Both non-pocket and pocketed orifice type restrictors are considered and the flow characteristics in the bearing clearance are investigated.The analysis results indicate that the occurrence of the vortex flow causes the bearing micro-vibration.Through analysis,the occurrence condition of the vortex flow is illustrated.For the non-pocket orifice type restrictor,the occurrence of the vortex flow is attributed to the occurrence of the supersonic region and shock waves in the flow field.For the pocketed orifice type restrictor,the vortex flow always exists.To suppress the vortex flow,for the bearing with non-pocket orifice type restrictor,the maximum Mach number in flow field should be controlled below 1.For the bearing with pocketed orifice type restrictor,the maximum Reynolds number should be kept as small as possible.Moreover,the way to suppress the vortex flow provides a physics base for modeling the bearing parameters design optimization.Also,the micro-vibrations of the bearings with a single non-pocket or pocketed orifice type restrictor are compared.The comparison shows that the micro-vibration amplitude of the pocketed type bearing is larger one order of magnitude than that of the nonpocket one.The analytical-CFD combined method.A kind of analytical-CFD combined methods is proposed for calculations of the aerostatic journal bearing static and dynamic performances.The combined method compromises both advantages of the traditional analytical method and the modern CFD numerical method.Both static and dynamic mechanical performances can be calculated accurately with acceptable computational expense.The analytical-CFD combined method makes the bearing parameters design optimization realizable.The influence rules of journal bearing parameters on performances are discussed by use of the combined method.The results show that the stiffness and damping of the air film are non-monotonic and nonlinear in the given design field,some of the mechanisms are illustrated.The multi-objective optimization method for the aerostatic journal bearing and its application.To eliminate the micro-vibration and get the optimum static and dynamic performances,the design optimization modeling method is studied.The considered design variables include structural parameters and air supply pressure.For the static performance,maximum load carrying capacity should be achieved.For the dynamic performances,the maximum displacement impedance should be achieved.The influence of the working condition on optimization results is discussed.In the considered engineering cases,the optimization results are compared,the comparison shows that the optimum load carrying capacity and displacement impedance change when the working condition changes,while the optimum points change less.With increase of the orifice number per circle,the optimum bearing performances are improved,but the improvement slows down.The proposed optimization modeling method can be used effectively in engineering bearing design.